Isotype-specific binding patterns of serum antibodies to multiple conformational epitopes of Bet v 1

Background: Birch pollen is an important elicitor of respiratory allergy. The major allergen, Bet v 1, binds IgE exclusively via conformational epitopes. Objective: We identified Bet v 1-specific epitope repertoires of IgE and IgG from birch pollen-allergic and nonallergic subjects. Methods: Chimeric proteins were created by grafting individual epitope-sized, contiguous surface patches of Bet v 1 onto a nonallergenic structural homolog and expressed in Escherichia coli. Binding of IgE, IgG1, and IgG4 from sera of 30 birch pollen-allergic and 11 nonallergic subjects to Bet v 1, 13 chimeric proteins, and 4 bacterial Bet v 1 homologs were measured by ELISA. The proportion of epitope-specific in-total Bet v 1-specific IgE and the cross-reactivity of Bet v 1-specific IgE with bacterial homologs were determined by competitive ELISA. Results: Thirteen soluble, correctly folded chimeric proteins were produced. IgE from 27 of 30 birch pollen-allergic patients bound to 1 to 12 chimeric proteins (median, 4.0), with patientspecific patterns evident. Three chimeras binding IgE from the majority of sera were identified, the grafted patches of which overlapped with previously published epitopes. Patterns of IgG1 and IgG4 binding to the chimeric proteins did not correspond to the binding patterns of IgE. Sera of 19 of 30 birch pollenallergic patients contained low amounts of IgE to bacterial homologs. Bacterial proteins were able to partially inhibit IgE binding to Bet v 1. Conclusion: Epitopes recognized by Bet v 1-specific antibodies from birch pollen-allergic patients are specific to each patient and differ between IgE, IgG1, and IgG4.